This invention relates generally to panel structures of building materials such as roof paneling and side paneling members in sheet and thin-plate structures of railway rolling stock, ships, buildings, and other structures. More particularly, the invention relates to a method of fabricating panel structures of the above stated character and of the type comprising a skeletal framework and an outside or skin plate secured to the framework in a manner to prevent welding deformations in the skin plate.
In recent years, there has been a great demand for reductions in structural weights, particularly in railway rolling stock, and, in accordance with this demand, there has been progress in the reduction of wall thicknesses of the structural members (panels) of vehicular structures. In the case of steel materials, in general, the thin wall thicknesses of skin plates are of the order of 1.2 to 1.6 mm., while those of framework members are of the order of 2.3 to 4.5 mm. As a consequence of this trend toward reduced thicknesses, the occurrence of deformations at the time of assembly of the constituent members (e.g., roof paneling members and side paneling members) in thin plate structures as mentioned above has been unavoidable.
Of the kinds of deformations which thus occur, approximately 50 percent is a "sagging" of skin plates, which is a buckling form of deformation peculiar to thin plate structures, while approximately 40 percent is an "irregular passage (bending)". These two kinds of deformation make up 90 percent of all deformations. The "sagging" of skin plates includes local strains due to rolling during the production of these plates and strains due to welding. For this reason, when a skin plate of the character referred to above is secured to a grid-like framework by a process such as welding, various kinds of deformations in the form of concavities and convexities are produced in the individual rectangular bays or unit grid frames of the skin plate.
Heretofore, these convex-concave deformations have been removed by a deformation removal process which comprises local heating (for example, point heating or line heating) of each bay after fabrication of a panel and thereafter rapidly cooling the same. The work in man-hours required for this deformation removing work has been found to be a tremendous 20 to 25 percent of the work for assembling a vehicle body and thereby entails a great amount of labor and other cost.
Moreover, in the case of stainless steel plate materials, deformation removal cannot be carried out because heated parts become colored, whereby the panel looses its commercial value. For this reason, stainless steel plates are used in the form of corrugated skin plates although this form is expensive and looses some aesthetic value. Furthermore, in the case of aluminum materials, since their thermal conductivity is good, the efficiency of the work of deformation removal by point heating is poor, and deformation cannot be removed in some cases. Accordingly in the present state of the art, complicated work procedures using such means as auxiliary cooling plates are resorted to in producing aluminum material panels.
It has heretofore been considered that, as mentioned above, the occurrence of welding deformations in thin plate structures is unavoidable, and in all previous methods, suitable deformation removal work was carried out after the deformations developed.